The present invention relates to a data recording apparatus and method and a recording medium. In particular, the invention relates to a data recording apparatus and method suitable for recording data onto a recording medium such as a phase-change disk by forming marks and spaces thereon, as well as to such a recording medium.
The phase-change disk now attracts much attention as a next-generation high-density recording medium. Information recording onto a phase-change disk is performed by utilizing the property (phase change) of a recording film that it is rendered in an amorphous state when heated to a given temperature (for instance, about 600.degree. C.) higher than the melting point and then rapidly cooled and is recrystallized when heated to a temperature (for instance, about 400.degree. C.) lower than the melting point and then slowly cooled, as shown in FIG. 1. Recorded information is reproduced by utilizing the fact that the reflectance of light in the amorphous state is different than in the crystal state. An amorphous portion and a crystal portion are usually called a mark and a space, respectively. Thus, it can be said that information recording onto a phase-change disk is performed by forming thereon marks and spaces that correspond to information.
Incidentally, as for the magneto-optical disk as typified by Mini-Disc (trademark), the magnetic modulation scheme enables direct overwriting but is hard to provide high-speed recording and reproduction. On the other hand, although the optical modulation scheme enables high-speed recording and reproduction, to realize direct overwriting it requires use of a special recording film.
In contrast, with the phase-change disk, direct overwriting in which erasure of recorded data and recording of new data are effected simultaneously can easily be realized by forming marks and spaces while switching between medium power (erasing level) and high power (recording level, i.e., writing level) as shown in FIG. 2. Recorded data are reproduced by illuminating the disk with laser light of such low power (reproduction level) that no phase changes occur in a recording film. More specifically, based on the fact that marks in the amorphous state have a small reflectance while spaces in the crystal state have a large reflectance, data are reproduced by using differences in the quantity of reflection light that is obtained by illuminating the disk with laser light.
In addition to the above-mentioned advantage that direct overwriting can easily be realized, the phase-change disk are advantageous over the magneto-optical disk in the following points. These advantages are favorable for increasing the recording density.
(1) The structure of a pickup (optical pickup) can be made simple. PA1 (2) A reproduction signal has a large amplitude and a large C/N ratio (carrier to noise ratio). PA1 (3) Since a recording layer has small heat conductivity and a high erasing temperature, marks on adjacent tracks hardly influence each other and hence a high track density can be attained. PA1 (4) It is possible to obtain high signal intensity from minute marks by reproducing data by utilizing not only a difference in reflectance but also a difference between phases of reflection light beams.
The data recording onto the phase-change disk is purely thermal recording. Therefore, to realize high-density recording, the heat management during data recording and erasure is most important.
As for the data recording scheme for the phase-change disk, the mark edge recording scheme is known in which marks and spaces of various lengths are formed and information is allocated to lengths of both marks and spaces. In the mark edge recording scheme, there may occur a case that laser light of the recording level is applied for a long time to form a relatively long mark. In such a case, due to the heat accumulation effect of a recording film, a tear-shaped mark is formed which is thicker in the disk radial direction in the latter half portion. Since the rear edges of such tearshaped marks are deviated from the ideal positions, the error rate becomes high when they are reproduced.
There is known a recording scheme A in which to prevent the radial width of a mark from increasing in its latter half portion, the illumination light quantity is reduced for the latter half portion by multipulse-driving a light-emitting means such as a laser diode that emits laser light.
In the recording scheme A, with an assumption that T represents a pulse width corresponding to one clock (data rate) as shown in FIG. 3A, a mark having a length nT (n: integer) is formed by driving a laser diode with a signal A that is expressed by Equation (1). (In the following, a signal for driving a light-emitting means such as a laser diode is referred to as recording pulses, where appropriate.) EQU A=1.5M+(n-2)(0.5S+0.5M)+0.5S (1)
where M means a H-level portion having a length T and S means a L-level portion having a length T. (Conversely, M and S may be made to correspond to the L-level and the H-level, respectively.)
Thus, for example, when data (see FIG. 3B) is 2M, that is, when n=2, according to Equation (1) the laser diode is driven with recording pulses A of 1.5M+0.5S, i.e., a H-level (recording level) portion of 1.5T and a L-level (erasing level) portion of 0.5T, as shown in FIG. 3C. When data (see FIG. 3B) is 3M. that is, when n=3, the laser diode is driven with recording pulses A of 1.5M+0.5S+0.5M+0.5S as shown in FIG. 3C. Similarly, when data (see FIG. 3B) is 5M, that is, when n=5, the laser diode is driven with recording pulses A of 1.5M+3(0.5S+0.5M)+0.5S (=1.5M+0.5S+0.5M+0.5S+0.5M+0.5S+0.5M+0.5S) as shown in FIG. 3C.
In the recording scheme A (and also in a recording scheme B (described later)), a recording pulse A corresponding to a portion nS of data is made nS.
However, the recording scheme A has a problem that the illumination light quantity becomes small at latter half portions of marks and a thermally unstable state occurs at their rear edges. In particular, when the linear velocity is high in the recording, the positions of the rear edges have remarkable variations.
To solve the above problem, a recording scheme B has been proposed in which a relatively large quantity of light is applied in forming the end portion of a mark, as disclosed in Furumiya et al., "Studies on a high recording rate, high-density recording scheme for phase-change disks," ITE Technical Report, Vol. 17, No. 79, pp. 7-12, VIR '93-83, December 1993 (hereinafter referred to as Reference 1), Japanese Unexamined Patent Publication No. Hei. 6-295440 (Reference 2), and Japanese Unexamined Patent Publication No. Hei. 7-129959 (Reference 3), for instance.
In the recording scheme B, a mark having a length nT is formed by driving a laser diode with recording signal (pulses) B that is represented by EQU B=1.0M+(n-2)(0.5S+0.5M)+0.5M+0.5S. (2)
Therefore, for example, when data (see FIG. 3B) is 2M, that is, when n=2, according to Equation (2) the laser diode is driven with recording pulses B of 1.0M+0.5M+0.5S=1.5M+0.5S as shown in FIG. 3D. When data (see FIG. 3B) is 3M, that is, when n=3, the laser diode is driven with recording pulses B of 1.0M+0.5S+0.5M+0.5M+0.5S=1.0M+0.5S+1.0M+0.5S as shown in FIG. 3D. Similarly, when data (see FIG. 3B) is 5M, that is, when n=5, the laser diode is driven with recording pulses B of 1.0M+3(0.5S+0.5M)+0.5M+0.5S (=1.0M+0.5S+0.5M+0.5S+0.5M+0.5S+1.0M+0.5S) as shown in FIG. 3D.
However, even the recording scheme B has a problem that thermal interference occurs in portions where short marks and spaces such as those of 2T and 3T, in particular, between marks that are separated by a short space. As a result, edge positions are deviated from the ideal positions, which in turn increases the error rate.
To solve the above problem, References 1 and 3 disclose a recording compensation method in which recording is performed while edge positional deviations due to thermal interference etc. are compensated by detecting data corresponding to short marks and spaces and changing the positions of front edges and rear edges of recording pulses corresponding to such data.
FIG. 4 shows the configuration of an example of a conventional recording compensation circuit that performs the above type of recording compensation.
Modulated data (see FIG. 3B) obtained by modulating recording information are supplied to a front end pulse generator 101, a gate generator 102, a rear end pulse generator 103, and a mark/space length detector 104.
The modulated data are obtained by modulating information by combining (1, 7) RLL (run length limited) and NRZI (non-return-to-zero inverted), and hence do not include any isolated inversion. Further, the minimum inversion width and the maximum inversion width of the modulated data are 2 and 8, respectively (n is in a range of 2 to 8 in Equation (2)).
The front pulse generator 101 generates a front end pulse having a pulse width 1T (corresponding to the first term 1.0M of the right side of Equation (2)) that rises at a position delayed by 0.5T from the rising edge of each modulated data. The front end pulse is supplied to an OR gate 110 via a delay line 108.
The gate generator 102 generates, based on each modulated data, a gate signal whose pulse width corresponds to n in Equation (2), and supplies it to one input terminal of an AND gate 109. A clock signal (see FIG. 3A) is supplied to the other input terminal of the AND circuit 109. Thus, the AND circuit 109 calculates the logical product of the clock signal and the gate signal, thereby generating burst pulses, which correspond to a result obtained by deleting the last 0.5M from the second term (n-2)(0.5S+0.5M) of the right side of Equation (2). The burst pulses are supplied to the OR gate 110.
The rear end pulse generator 103 generates a rear end pulse having a pulse width 1T (corresponding to a combination of the last 0.5M of the second term (n-2)(0.5S+0.5M) and the third term 0.5M of the right side of Equation (2)) that falls in synchronism with the falling edge of each modulated data. The rear end pulse is supplied to the OR gate 110 via a delay line 107.
The OR gate 110 calculates the logical sum of the front end pulse, the burst pulses, and the rear end pulse, and thereby generates and outputs recording pulses B (see FIG. 3D) that are given by Equation (2).
On the other hand, the mark/space length detector 104 detects modulated data corresponding to short marks and spaces such as those of 2T and 3T, and supplies a detection result to selectors 105 and 106. Based on the detection result of the mark/space length detector 104, the selectors 105 and 106 determines delays to be applied to the front end pulse and the rear end pulse, respectively. The delay lines 108 and 107 are informed of the thus-determined delays.
The delay lines 108 and 107 output the front end pulse and the rear end pulse after delaying those by the delays the information of which has been given by the selectors 105 and 106, respectively.
In the above manner, recording compensation for edge positional deviations due to thermal interference etc. is effected by changing the positions of front end edges and rear end edges of recording pulses corresponding to data that correspond to short marks and spaces.
Incidentally, with the optical disk, the magneto-optical disk, and the like, data are recorded according to the CAV (constant angular velocity) scheme. In the CAV scheme, in which the angular velocity (disk rotation speed) is constant, the linear velocity is high on the disk inner side and low on the disk outer side if the data rate is constant. As a result, the total recording capacity is small.
On the other hand, where data are recorded according to the CLV (constant linear velocity) scheme, in which case the linear velocity is constant, the linear density is constant if the data rate is constant. As a result, the total recording capacity can be made large. However, the CLV scheme requires a complex control system because the rotation speed of a spindle motor for rotating a disk needs to be varied continuously over the entire disk from the innermost track to the outermost track.
In view of the above, the MCAV (modified CAV, or MZ-CAV (multi-zone CAV)) has been proposed which has both of the advantage of the CAV scheme (rotation driving at a constant angular velocity, i.e., simple control) and the advantage of the CLV scheme (large recording capacity).
In the MCAV scheme, rotation driving is performed at a constant linear velocity as in the case of the CAV scheme. However, a disk is divided into a certain number of (for example, about 50) zones from the innermost track to the outermost track, and recording is performed such that the data rate increases as the zone goes outward. The data rate is controlled so that the linear densities at the innermost tracks of the respective zones become identical. Thus, the recording capacity can be made large as in the case of the CLV scheme.
To realize high-density recording by using the phase-change disk, from the viewpoint of recording compensation it is preferable to employ the CLV scheme (linear velocity is constant) because recording compensation of fixed form can accommodate it. That is, since the data recording onto the phase-change disk is purely thermal recording, recording compensation of fixed form is sufficient if the linear velocity is constant.
However, in the CLV scheme, at the occurrence of a traverse (track jump), the disk rotation speed needs to be changed from a value suitable for a position before the traverse to a value suitable for a position after the traverse. Data reproduction cannot be restarted until the track rotation speed reaches the latter value. Although the random access capability is an important feature of disk-shaped recording media which feature is absent in tape-shaped media, the CLV scheme has a disadvantage of slow random access speed.
One way to prevent uses of the phase-change disk from being restricted by the above disadvantage is to employ the MCAV scheme which can provide large recording capacity and enables high-speed random access.
However, it is difficult for recording compensation of fixed form to accommodate the MCAV scheme because the linear velocity varies from the innermost track to the outermost track.